1. Field of the Invention
The present invention is an apparatus for removing a thrombus or other blockage from an artery or other vessel. More specifically, the apparatus comprises a microcatheter containing a micro piezo electric fiber that generates shear flows capable of disrupting and removing blood clots in small blood vessels that are difficult or impossible to reach with conventional thrombectomy catheters. The shear forces required for thrombus disruption are produced through a tube effect created by the positioning of one or more piezo transducers relative to the opening of a tube or catheter head.
2. Description of Related Art
Currently known techniques for emulsifying and removing obstructions from arteries include the use of high velocity saline jets, pulsed laser emissions, direct mechanical disruption, and acoustic vibration. Descriptions of these techniques may be found in U.S. Pat. Nos. 6,676,6317; 6,719,718; 6,805,684; 6,875,193; 6,558,366; 6,368,318; 6,685,722; 6,767,353; 6,824,551; and 6,379,325, which are incorporated by reference in their entirety.
The foregoing techniques suffer from one or more the following drawbacks including damage to the arterial walls, blocking of smaller, downstream arteries with clot fragments, and catheter diameters limited to use in large arteries. Laser devices and photo-acoustic devices in which light energy is converted into acoustic waves generate excessive heat and can perforate arterial walls. Saline jets can cause vessel dissection. Removing obstructions by suction can also damage arterial walls.
Ultrasound technology has been developed to open blocked or restricted arteries. The following examples of this technology are incorporated by reference in their entirety. U.S. Pat. No. 6,024,718 discloses an ultrasound catheter that uses a piezoelectric element to generate ultrasonic energy to emulsify a thrombus via sonophoresis. The piezoelectric element in this device is located at the tip of the catheter and is shaped to provide the desired ultrasonic field. U.S. Pat. No. 6,398,792 discloses an angioplasty catheter tipped with an ultrasonic transducer to cause dissolution of a thrombus and to crack and soften the surrounding plaque. The ultrasonic waves form the transducer are localized to a selected portion of the artery by inflating a balloon downstream of the transducer. US 2002/0003355 describes an apparatus comprising a catheter tipped with a substrate that has one or more piezoelectric elements attached to the substrate's outer surface. US 2002/0133111 describes a neuro-thrombectomy catheter that uses transducers distributed along the catheter length to move fluid and debris through the lumen. The movement of fluid generates suction at the tip of the catheter that pulls a thrombus into the catheter lumen, where it is emulsified. US 2002/0151825 describes an atherectomy catheter that uses ultrasonic waves generated by a piezoelectric transducer coupled to a conically-shaped tip to emulsify a plaque or thrombus. US 2004/0171981 discloses a device for removing an occlusion from an artery using an elongated, flexible ultrasonic probe at the distal end of a catheter in conjunction with a thrombolytic drug. Transverse ultrasonic vibrations generate a “cavitational energy” that extends radially outward from the longitudinal axis of the probe to ablate the occlusion.
None of the devices described above use a piezo transducer positioned relative to a tube specifically to generate a tube effect resulting in acoustic streaming.
U.S. Pat. No. 6,139,543 and U.S. Pat. No. 6,547,779 disclose a flow apparatus for the disruption of clots and other occlusions in blood vessels. This device uses pulsed laser light to generate small, transient bubbles that alternately expand and collapse to pump fluid near the tip of a capillary, or small diameter catheter. Proper arrangement of optical fibers relative to the open end and side windows of the catheter tip generates a fluid flow in which fluid is ejected from the open end of the catheter tip and suctioned back into the catheter tip through the side windows. The '543 and '779 patents, incorporated by reference in their entirety, disclose that the flow apparatus can be used to remove obstructions by pushing the catheter tip through an obstruction and emulsifying it as it is suctioned into the side windows of the catheter. Alternatively, the fluid ejected from the tip of the catheter can be used to ablate an obstruction by placing the open end of the catheter against the surface of the obstruction. This device provides a means for disrupting obstructions in small arteries and is capable of generating fluid forces capable of disrupting clots.
The use of laser light to generate fluid streaming, as described in '543 and '779 patents, is distinct from the acoustic streaming produced by, the present invention. Laser-induced fluid streaming involves the localized heating and boiling of liquid to form bubbles that rapidly collapse. Pulsing the laser causes the repeated rapid formation and collapse of gas bubbles in liquid and generates excess heat in the process.
The present invention uses piezoelectric transducers to generate acoustic streaming of fluid capable of disrupting clots and other obstructions in arteries and other vessels without generating excessive heat or bubbles. Acoustic streaming has thus far been incapable of generating shear forces strong enough to disrupt clots in small vessels. The present invention overcomes the previous limitations of acoustic streaming in small vessels using combinations of vibrational modes and catheter head configurations that use an unexpected tube effect to generate enhanced acoustic streaming.